1221561 has 24 divisors (see below), whose sum is σ = 2000544. Its totient is φ = 738720.

The previous prime is 1221559. The next prime is 1221589. The reversal of 1221561 is 1651221.

It is not a de Polignac number, because 1221561 - 2¹ = 1221559 is a prime.

It is a super-2 number, since 2×1221561² = 2984422553442, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (1221541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2445 + ... + 2901.

It is an arithmetic number, because the mean of its divisors is an integer number (83356).

2^1221561 is an apocalyptic number.

1221561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1221561 is a deficient number, since it is larger than the sum of its proper divisors (778983).

1221561 is an equidigital number, since it uses as much as digits as its factorization.

1221561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 483 (or 471 counting only the distinct ones).

The product of its digits is 120, while the sum is 18.

The square root of 1221561 is about 1105.2425073259. The cubic root of 1221561 is about 106.8985266766.

Adding to 1221561 its reverse (1651221), we get a palindrome (2872782).

The spelling of 1221561 in words is "one million, two hundred twenty-one thousand, five hundred sixty-one".